The present invention relates to the design and construction of a temperature compensating system for a closed fluid-based system such as a damping system. More particularly, the present invention relates to a temperature compensating system adapted for compensating for increases in damping fluid volume due to temperature changes in a fluid damped suspension system so as to maintain a steady pressure within the damping system.
In the past, suspension systems have been used for various applications, including for cushioning impacts, vibrations, or other disturbances experienced by vehicles and machinery. Typical applications, for example, include the use of suspension systems in bicycles and motorcycles.
For example, bicycles have been developed with suspension systems for cushioning impacts or vibrations experienced by the rider when the bicycle contacts bumps, ruts, rocks, pot holes, or other obstacles in the path over which the bicycle is ridden. Typically, such bicycle suspension systems may be configured for use in the front or rear bicycle fork, in the head tube that connects the front fork to the bicycle frame and handlebars, in the seat post, in conjunction with a swing-arm assembly, or in another position along the bicycle frame.
Bicycle suspension systems typically include a pair of telescoping tubes (an inner tube and an outer tube) containing one or more biasing elements that oppose the compressive or expansive motion of the telescoping tubes. The biasing elements typically are spring devices such as coil springs, elastomer springs, gas springs such as air springs, among other types of springs. The biasing elements are placed within one or more of the tubes for biasing the tubes apart from each other. Using biasing elements in this way permits the tubes to compress in response to an impact or other force input, and expand or rebound once the force is removed, so that the inner and outer tubes return to their original spaced apart positions relative to each other.
Bicycle suspension systems have also included damping systems using generally incompressible fluids such as hydraulic oil, water, fish oil, and glycerine, among others, or a combination thereof. The damping systems act to absorb some of the energy of an impact or other force input causing compression or rebound of the tubes so that a more controlled response of the bicycle to force inputs may be achieved.
Exemplary closed fluid damping systems for bicycle suspension forks are described in U.S. Pat. No. 5,456,480 to Turner and U.S. Pat. No. 5,445,401 to Bradbury. The damping systems disclosed in Turner and Bradbury use hydraulic oil as the damping medium and include a piston and valve assembly. The oil, piston and valves are contained in a closed, or fixed-volume, cartridge system. When the telescoping members of the bicycle compress and/or expand, the oil is forced through restrictive orifices in the piston and valve assembly.
In general, a fluid damping system opposes motion by converting the energy of compressive or expansive motion into heat. This heat raises the temperature of the damping fluid in the system. For example, on a fairly cool day, the temperature within a typical damping system typically may reach approximately 110.degree. F., and may go up to approximately 180.degree. F. on hotter days. As the temperature of the damping fluid increases, the volume of the damping fluid expands. In a closed or fixed-volume damping system, an increase in fluid volume is problematic, as it tends to pressurize the oil in the system and even force oil out of the system causing undesirable leaking and, potentially, the irreversible failure of the system such as occurs when the damping seals are forced to roll outward from their proper positions. In addition, once the oil contracts to its nominal volume, the efficiency of the damping system will be reduced by the introduction of air to the system. Even where the closure of the system is not compromised, the pressurization and depressurization of the system has a deleterious effect on the seals and other damping components. Thus, there is a need for a damping system having a temperature compensating device that, when used in a fixed-volume, incompressible damping system cartridge, is able to compensate for increases in volume of the damping fluid caused by fluid temperature increases.
A temperature compensator that does not yield sufficiently to the expanding fluid may not be able to reduce the internal pressure of the damping system to an acceptable level. As a result, there is a need for a temperature compensating device for a fluid damping system of a suspension system that effectively reduces the internal pressure of the damping system created as temperatures therein increase and thereby tends to maintain a stable pressure in the system.
At the same time, the temperature compensating system should not yield too readily. A temperature compensating system that yields too easily in response to increases in damper fluid volume may reduce the effectiveness of the damper. For example, upon compression or expansion of the system, the oil may merely compress the temperature compensator instead of being forced through the valve assembly, thus rendering the valving ineffectual. Accordingly, there is a need for a temperature compensating system for a fluid damper of a suspension system that does not reduce the effectiveness of the damping system. There is a related need for a temperature compensating system that compensates for temperature changes within a damping system yet also permits steady damping control and thereby maintains consistent system performance.